The present invention relates to a device for manufacturing plastic items, particularly caps for closing containers.
Devices for the compression molding of caps (closures) for closing containers are known which comprise a carousel which can rotate about a vertical axis and whereon a plurality of angularly equidistant molding units are fitted. Each unit comprises an upper male mold part which is aligned with a lower female mold part. During the rotation of the carousel, a dose of plastic material in the pasty state is introduced in the female mold part and is pressed by means of a mutual movement of the two mold parts. Devices of the described type are known for example from PCT/EP95/03644 by the same Applicant.
In devices of the indicated type it is also known to provide, in the upper mold part, cooling means which are meant to cool the forming punch and ejection means which remove the cap once molding has been completed.
In order to ensure removal of the cap from the forming punch, the mechanical ejecting action applied to the caps is assisted by a pneumatic action applied by injecting compressed air inside the caps; said air, by inflating the caps, separates them from the surface of the punch, improving the effectiveness of the mechanical action.
Currently, the pneumatic action is not utilized advantageously owing to the fact that the compressed air, in its path leading to the ports for injection inside the cap, must pass through many interstices and cavities which reduces its effectiveness and delay its action on the caps. In order to obviate these drawbacks, i.e., recover promptness in intervention and increase the flow-rate of the air, it is necessary to provide high pressure values, with consequent difficult management of the effects on the product, such as deformations and unevenness of the walls.
Moreover, the pneumatic action, as conceived in current devices, contaminates the molded item, since the conveyed air entrains particles of the fluid used to lubricate the moving parts of the upper mold part. A further drawback is constituted by the fact that the moving parts of the upper mold part produce a xe2x80x9cpistonxe2x80x9d effect which often produces unintended movements of some mechanical components.
Differently from compression-molding devices, injection-molding devices expel the items mainly by mechanical methods and therefore with a high risk of damaging the products.
The aim of the present invention is to improve the operation of devices of the described type, substantially obviating the above described shortcomings and allowing assured removal of the items from the mold.
This aim is achieved with an apparatus whose characteristics are defined in the appended claims.